Respiratory infection with Francisella. tularensis is the deadliest form of disease and represents the most likely route to be used by bioterrorists. Although mucosal surfaces represent the first line of defense against pneumonic tularemia, little is known about protective immunity at this site. The objective of this subproject is to examine the importance of various immune mechanisms in defense against respiratory F. tularensis infection and to design effective strategies for induction of protective lung immunity. In Specific Aim 1, various mouse strains with defined genetic disruptions will be exploited to examine the roles of Fc receptors (FcR), IgA, T cell subsets, and cytokines in infection outcome. The specific animals to be used for this purpose will include unique mouse strains that lack the FcRgamma, chain, the polymeric Ig receptor, the neonatal FcR, IgA,alpha-beta versus gamma-delta T cells, CD4 versus CD8 cells, and selected cytokines. In Specific Aim 2, the ability to induce protective mucosal immunity after intranasal vaccination with killed F. tularensis or F. tularensis subunit vaccines will be examined using IL-12 as a vaccine adjuvant. Protection will be assessed by measuring antibody and cytokine expression, and by direct intranasal or inhalation challenge, followed by monitoring survival and bacterial carriage in the infected mice. Finally, experiments conducted in Specific Aim 3 will determine the ability of F. tularensis antigens specifically targeted to FcR to induce protective mucosal and systemic immunity. In all cases, we will measure the induction and effectiveness of humoral versus cell-mediated immunity. Initial experiments will be performed with the F. tularensis live vaccine strain, which is virulent for mice but not humans, followed by studies with the human Schu4 virulent strain. The results of this subproject will for the first time define the pulmonary immune mechanisms that are responsible for protection against pneumonic tularemia and allow the design of new mucosal vaccination strategies for effective biodefense against F. tularensis.